Displacement pumps may be used to dispense liquids in precise volumes. One type of displacement pump may include a ceramic displacement piston that reciprocates within a pump chamber in a ceramic cylinder to cause liquid to be drawn in and expelled from the pump while a valve piston rotates between one or more inlets and one or more outlets. In such pumps, the pump chamber may be primarily sealed by a tight fit between the displacement piston and the cylinder.
In certain applications, the liquid being dispensed may include solids in solution and the solid may precipitate from the solution causing problems. In certain medical applications, for example, EDTA/salt solutions may be dispensed and salt crystals may be formed when the solution migrates from the pump chamber and dries. The salt crystals may cause contamination of the pumping area and/or may cause the pumps to seize. Although pumps have been provided with washing features, such existing pumps may not adequately wash the piston and seals, particularly where a tight fit is used to seal the piston and cylinder.